1. Field of the Invention
The present invention relates to a transmitting circuit, communication equipment, an audio equipment, a video equipment, and a transmitting method used in a radio apparatus such as a mobile phone, a wireless local area network (WLAN) and the like.
2. Related Art of the Invention
One example of a conventional transmitting circuit (for example, see Japanese Patent Laid-Open Publication No. 2002-325109) is shown in FIG. 27.
The conventional transmitting circuit consists of a data generator 1501, a delta sigma modulator 1502, a power source control unit 1503, an angle modulator 1504, an amplitude modulator 1505, a filter 1506, and an output terminal 1507.
The data generator 1501 is a circuit which outputs an amplitude data and a phase data.
The delta sigma modulator 1502 is a circuit, which delta-sigma-modulates an inputted data, and outputs a data lower in resolution than the inputted data, that is, a data lower in the number of the voltage value to be obtained.
The power source control unit 1503 is a circuit which outputs a voltage proportional to an input signal.
The angle modulator 1504 is a circuit which angle-modulates a carrier wave with a phase data.
The amplitude modulator 1505 is a circuit which amplitude-modulates an angle-modulated wave with a signal supplied from the power source control unit 1503.
The filter 1506 is a circuit which removes an unnecessary frequency component from among input signals.
The output terminal 1507 is a terminal for obtaining an output signal.
Next, the operation of the conventional transmitting circuit will be described.
The amplitude data and the phase data are outputted from the data generator 1501. The amplitude data outputted from the data generator 1501 is delta-sigma-modulated by the delta sigma modulator 1502, and is inputted to the power source control unit 1503. The power source control unit 1503 outputs a voltage proportional to the input signal. In the meantime, the phase data outputted from the data generator 1501 is angle-modulated by the angle modulator 1504, and is inputted to the amplitude modulator 1505. The amplitude modulator 1505 amplitude-modulates an angle-modulated wave with the signal supplied from the power source control unit 1503. A quantization noise generated by the delta sigma modulator 1502 is removed by the filter 1506, and is outputted from the output terminal 1507.
By using such a conventional transmitting circuit, it is expected that the effects of nonlinearity of an amplifier can be minimized, and an efficient circuit which needs little consumption power is provided.